The objectives are to select and propogate somatic cells having specific physiological mutations. Normal cells of investigative interest will be cloned to provide homogeneity with respect to the stage of differentiation, genetic composition, etc. Mutants will be selected from natural populations or after treatment of cells to induce mutations. Selections will be made for specific functional or metabolic defects. Mutants of a functional class will be characterized by biochemical and/or genetic analysis. Mutants will be propagated to a sufficiently large population to enable proper distribution with a minimum of 25 vials of 1 ml capacity, processed for preservation, and stored in liquid nitrogen. Samples from frozen aliquots will be checked by the contractor for viability and relative stability of the mutant phenotype.